Hepatitis C, originally called non-A, non-B hepatitis, was first described in 1975 as a disease serologically distinct from hepatitis A and hepatitis B (Feinstone, S. M. et al. (1975) N. Engl. J. Med., 292:767-770). Although hepatitis C was (and is) the leading type of transfusion-associated hepatitis as well as an important part of community-acquired hepatitis, little progress was made in understanding the disease until the recent identification of hepatitis C virus (HCV) as the causative agent of hepatitis C via the cloning and sequencing of the HCV genome (Choo, A. L. et al. (1989) Science, 288:359-362). The sequence information generated by this study resulted in the characterization of HCV as a small, enveloped, positive-stranded RNA virus and led to the demonstration that HCV is a major cause of both acute and chronic hepatitis worldwide (Weiner, A. J. et al. (1990) Lancet, 335:1-3). Subsequently, it has been observed that approximately 80% of individuals acutely infected with HCV become chronically infected and more than 20% of these individuals eventually develop liver cirrhosis (Alter, H. J. Seeff, L. B.: Transfusion Associated Hepatitis, In: Zuckerman, A. J. Thomas, H. C. (eds): Viral Hepatitis: Scientific Basis and Clinical Management. Edinburgh Churchill Livingstone, 1993). In addition, a strong association has been found between HCV infection and the development of hepatocellular carcinoma (Bukh et al. (1993) Proc. Natl. Acad. Sci. USA, 90:1848-1851) and HCV infection also seems to be associated with other diseases, including some autoimmune diseases (Manns, M. P. (1993) Intervirol., 35:108-115; Lionel, F. (1994) Gastroenterology, 107:1550-1555). Thus, significant morbidity and mortality is caused by HCV infection worldwide and vaccine development is a high priority.
Choo et al. ((1994) Proc. Natl. Acad. Sci. USA, 91:1294-1298), using recombinant E1 and E2 proteins of HCV-1 as immunogens, reported the successful vaccination of chimpanzees against challenge with 10CID.sub.50 of the homologous strain of HCV. However, Choo et al. did not demonstrate protection against challenge with a heterologous strain of HCV and the recent discovery of the extraordinary diversity of HCV genomes based on sequence analysis of numerous HCV isolates (Bukh et al.; Proc. Natl. Acad. Sci. USA, (1993) 90:8234-8238, Bukh et al. (1994) Proc. Natl. Acad. Sci. USA, 91:8239-8243) suggests that a successful vaccine must protect against challenge by multiple strains of HCV. In addition, both Farci et al. (Farci, P. et al. (1992) Science, 258:135-140) and Prince et al. (Prince, A. M. et al. (1992) J. Infect. Dis., 165:438-443) have presented evidence that while infection with one strain of HCV does modify the degree of the hepatitis C associated with the reinfection, it does not protect against reinfection with a closely related strain.
One possible candidate for use as a immunogen in a vaccine protective against multiple strains of HCV is a short region within the E2 gene termed hypervariable region 1 (HVR1) that has many similarities to the V3 loop of HIV, which represents the principal neutralizing domain of HIV (Letvin, N. L. (1993) N. Engl. J. Med., 329:1400). Indeed, the recent demonstration that antibodies specific to HVR1 can neutralize HCV in an in vitro binding assay (Zibert, A. et al. (1995) Virology, 208:653-661) suggests that HVR1 may be a principal neutralization determinant of HCV. Thus, the identification of HVR1 sequences from multiple HCV isolates of different genotypes may be useful in developing an immunogen capable of stimulating a protective immune response against challenge by infection with HCV isolates.